Many lobbyists are people who used to work in the government, either as elected officials, political appointees, staff for elected officials, or career civil servants. Their experience in their previous position(s) gives them a great deal of knowledge of how the government works, and a long list of personal contacts – especially in the area of government they used to work in. Former elected officials and political appointees (former members of Congress, Senators, department secretaries, etc.) also often carry a reputation that helps them open alot of doors.
Beyond their background, many lobbyists also share social and family lives with people that still work in the government. They often live in the same neighborhoods, go to the same churches, send their kids to the same schools, take classes at the same gyms, and eat at the same restaurants. So lobbyists often know alot of people in government in social circles as well. Lobbyists are often good friends with alot of the people they lobby, and those personal relationships are things that people who come from outside the beltway simply can’t duplicate.